DE3542410A1 - SEMICONDUCTOR LASER - Google Patents

Description

description

The invention relates to a semiconductor laser, and more particularly to a semiconductor interferometric laser with excellent Stability in the longitudinal mode vibration properties.

When a semiconductor laser is used as a light source for optical communication systems or for optical information systems is used, it is highly desirable that the device'a Performs stable oscillation that does not depend on the ambient temperature, the laser light output or that of a external system reflected laser beam is affected. When the oscillation of a semiconductor laser due to Changes of various factors is unstable, can induce mode influencing noise or by feedback, tes noise due to the interaction between the longitudinal laser modes and / or the longitudinal laser modes and the external fashions occur. Light transmission also leads using optical fibers leads to modal noise, seriously degrading the performance of the system leads.

To stabilize the vibration properties in longitudinal mode became different in the known semiconductor lasers Suggestions made. -

First, there are lasers with highly reflective mirrors Preventing reflected light from re-entering the laser and increasing internal optical density, which leads to a suppression of the non-laser-effective mode. However, these lasers have the disadvantage that they do not allow large light emission. Second, there are distributed Feedback lasers (DFB lasers) and distributed Bragg reflector lasers (DBR lasers), which contain a grating inside the waveguide. These lasers, which are powerful

Wave selectivity through the grid is possible excellent stability in longitudinal mode even with laser light turbulence. However, their manufacture is complicated and depends on the quality of the material used, so that they are not easy to manufacture. Third, there are C (cleaved coupled cavity) lasers, which are formed by using two semiconductor lasers or connects two waveguides in a line at their ends. These lasers are used to optically couple the two im To give the longitudinal mode laser stability. A disadvantage, however, is that it is difficult set up two lasers in such a way that they have good optical properties Coupling 'achieve and that a great technical skill is required to achieve stability in the longitudinal mode

"* ^{5 can be achieved} over a wide range by individually controlling the introduction of the carrier into the two lasers. Fourth, there are laser interferometers in which the whole of one or many reflective sections inside the waveguide of one semiconductor laser is constructed Waveguide can be divided into a number of parts and in which longitudinal mode stability is achieved by an interference effect between the longitudinal modes in each of these parts.A laser interferometer is described by Shyh Wang et al. In the TEEE-Journal on Quantum Electronics, Volume QE-18 , No. 4 on page 610, which appeared in 1982. This laser does not require a special manufacturing process if the internal reflective sections are easily manufactured

and the stability of the longitudinal mode is good. 30th

It is the object of the invention / to create a semiconductor laser which is improved over the prior art.

A semiconductor laser according to claim 1 serves to solve this problem. This overcomes the above-mentioned ones Difficulties as well as numerous other disadvantages of the prior art. It is a semiconductor laser interferometer with an effective built-in refractive index difference based on light absorption by a substrate between the part of the active layer which corresponds to the inner region of a strip-shaped channel which is on a surface of the substrate is formed and the part of the active layer which corresponds to the outer region of the channel, wherein Areas between the active layer and the substrate outside the channel along one in the active layer formed waveguide are formed, which corresponds to the channel, in the direction of the active layer to the substrate are different from each other and thereby make a difference in the effective refractive index between the parts of the form active layer that corresponds to the areas.

In a preferred embodiment, the active layer is a planar layer of uniform thickness.

In a preferred embodiment, the substrate has one second channel that intersects the first channel.

A current blocking device is preferably included in the Outside of the first channel formed on the substrate.

The invention thus creates (1.) a semiconductor laser, in particular an interferometric semiconductor laser with excellent stability in longitudinal oscillation mode due to an internal reflective section passing through a simple process in the waveguide of the active layer is formed j (2.) a semiconductor laser, in which by the Using a substrate with two types of strip-shaped Channels that cross on it, areas are formed between the active layer and the substrate, one

Difference between the active layer and the substrate there is a difference in the effective refractive index arises between the parts of the active layer, which corresponds to the areas, resulting in an internal Reflection section leads within a waveguide, which corresponds to the channel in the active layer.

The invention is explained in more detail below with reference to figures

explained? show it:
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Figure 1 is a perspective view of the substrate used to form a semiconductor laser;

Figures sectional views along the lines AA ¹ and BB ¹ 2a and b in Figure 1 for the case that a multilayer crystal for laser oscillation on the in Figure 1

substrate shown is formed;

Figures diagrams of the dependence of the built-in sub-3a and b different in the effective refractive index of the active ones

Layer of the thickness of the envelope layer \

FIG. 4 is a perspective view of an interferometric semiconductor laser; and

FIG. 5 shows a characteristic diagram of the dependence of the longitudinal vibration mode on the temperature for the semiconductor laser according to FIG. 4.

According to the invention, a reflective area is within of the waveguide of an index-guided semiconductor laser with built-in effective refractive index difference, which is based on a difference in light absorption by the substrate between the part of the active Layer corresponding to the interior of a channel formed on the substrate and the part of the active layer that corresponds to the outside of the channel, resulting in an interferometric laser that is excellent Has stability in a vibration longitudinal mode. The formation of a reflective area within

of the waveguide is made by the thickness of a part the lining layer, which is introduced between the substrate and the active layer outside the channel differs from that of the other respective part of the lining layer arranged along the waveguide, whereby there is a difference in the effective transverse index of refraction between the part of the active layer, which corresponds to the respective part of the cladding layer, and the other part of the active layer which corresponds to corresponds to the other part of the lining layer on the outside of the channel.

The invention is explained in more detail below with reference to the figures explained:

Figure 1 is a perspective view of the substrate 1 used for the formation of a semiconductor laser. Figures 2 (A) and 2 (B) are sectional views along the lines AA ¹ and BB ¹ according to Figure 1 in the case that on the substrate 1, on which strip-shaped channels X1 and Y1 intersect, a lining layer 2, an active one Layer 3, a lining layer 4 and a cover layer 5 are grown epitaxially one after the other, which are located to form a multilayer crystal with a double heterostructure for laser oscillation. According to FIGS. 2 (A) and 2 (B), the thickness cL 'of the part 22 of the lining layer 2, which lies between the substrate 1 and the active layer 3 in the outer region 9 of the channel X1, but in the inner region of the channel Y1 , greater than the thickness d. of the part 21 of the lining layer 22 which lies in the outer region 7 of both channels X1 and Y1. Figures 3 (A) and 3 (B) each show the relationship between the thickness d _{1 of} a part of the lining layer lying outside the channel X1 and the lateral difference in the effective refractive index Δη based on the difference in light absorption by the part of the substrate based within channel X1 or outside

- ο -

half of the channel X1, which indicates that a Thickness d. for part 21 of the lining layer in Figure 2 (A) of for example 0.1 µm and the thickness d .. 'of the part 22 the lining layer of Figure 2 (B) of, for example 0.5 to the effective refractive index difference Δη approximately

/ -ο -4

is equal to 10 in the area AA ¹ and 10 in the area BB ¹ , and accordingly laser light which is guided in the waveguide of the active layer 3 corresponding to the channel X1 is ^{partially in the area BB 1 of} the waveguide due to the change in the effective refractive index in the BB ¹ area reflected. According to the invention, the distribution of the distance between the substrate and the active layer is provided by the formation of the two kinds of channels X1 and Y1 which cross each other on the substrate to thereby form an internal reflective portion, resulting in an interferometric laser with excellent stability leads in a longitudinal vibration mode.

From the standpoint of stabilization in the transverse mode and / or decrease in emission loss in the reflective area according to FIGS Area is formed. In addition, if desired, a ² ^ current blocking function can be added to the reflective area, resulting in a structure that prevents the reflective area from obtaining gain, thereby making the internal reflective index more effective

to increase.
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example

Figure 4 shows an interferometric VSIS laser (V-channel

Inner strip substrate), which was manufactured as follows

en: On the (100) face of a p-GaAs substrate 11 was

an n-GaAs current blocking layer 12 having a thickness of

0.8 µm epitaxially grown from liquid phase. On that the current blocking layer 12 was etched by one strip-shaped V-channel X with a width of 4 µm in (01 f) -direction in such a way that channel X is the Substrate 11 reached. The current blocking layer 12 became further etched to form a further strip-shaped channel Y with a width of 3 µm and a depth of, for example 0.5 to form in the (011) direction in such a way that the channel Y does not reach the substrate 11. On the Substrate 11 with the channels X and Y located thereon became a lining layer 13 made of p-Ga., Al As, a active layer 14 made of p-Ga. “Al As, a lining layer 15 made of n-Ga Al As and a cover layer 16 made of n-GaAs successively epitaxially from the liquid phase grew up, which led to a multilayer crystal in a double heterostructure for laser oscillations. the The top of the p-liner layer 13 is flat and accordingly the active layer 14 is also flat and has a

uniform thickness.
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The part of the active layer 14 which corresponds to the channel X, acts as a built-in waveguide and the part of the active layer 14 corresponding to the section in which the channel X and the channel Y cross, acts as a reflective section.

As already mentioned, due to the on the substrate 11 formed channel Y is the thickness of the part of the lining layer 13, which is arranged outside the channel X but inside the channel Y, is larger than that of the other part of the lining layer 13 · which is arranged outside the channel X, so that the amount of light in the active Layer 14 to be absorbed by the substrate depending on the thickness of the part of the lining layer 13 (i.e., the distance between active layer 14 and substrate 11) fluctuates and causes a difference

in the effective index of refraction of the active layer 14, resulting in an internal reflective section in the waveguide the active layer 14 leads. The resulting VSIS interferometric laser has a cavity length of 250, um, divided by this reflective section in two Waveguide sections with lengths of 100 µm and 150 µm is divided.

This interferometric VSIS laser has a stabilized longitudinal mode that does not have a mode jump Experience a temperature range of about 15 C at ambient temperature, as can be seen from Figure 5, which the dependency the laser oscillation longitudinal mode shows temperature (where the oscillation threshold current is about 40 itiA at ambient temperature).

To improve stability in a vibrational longitudinal mode To obtain, it is appropriate that the internal reflective portion be used as a non-injection area is built by placing an n-GaAs current blocking layer in the section is formed in that the channel X and the channel ¥ cross each other on the substrate.

Although a GaAlAs system VSIS laser was previously described the invention is not limited thereto. Any semiconductor material and any known to those skilled in the art Current blocking mechanism can be used in accordance with the invention .

Claims (4)

Claims Interferometry vision semiconductor laser, marked through a built-in effective refractive index difference based on the absorption of. Light through a substrate, between the part of the active Layer that is within a strip-shaped channel which is formed on the surface of the substrate and the part of the active layer which is outside of the strip-shaped channel lies, with areas that between the active layer and the substrate outside the channel and along one in the active layer Are formed waveguide, which corresponds to the channel, at a distance from the active layer to the Substrate are different and therefore a difference in the effective refractive index between the parts of the active layer corresponding to the regions. 2. Semiconductor laser according to claim 1, characterized in that that the active layer is a planar layer of uniform thickness. 3. Semiconductor laser according to claim 2, characterized in that the substrate has a second channel which intersects the first canal. 4. Semiconductor laser according to claim 1 or 2, characterized in that a current blocking structure is applied outside of the first channel on the substrate.